Mars may usually spark questions about whether its ancient atmosphere was ever a haven for aliens, but when Mars spacecraft engineer Kristin Block eyed a rock caught in Curiosity’s wheel, she just had to wonder aloud on Twitter:
Turns out, not much of a racket at all.
Sorry to disappoint sci-fi fans and anyone obsessed with the movie The Martian, in which all sound on the Red Planet is heard as it is on Earth. Mars is actually much quieter than you’d imagine.
Suppose you could actually roam around the Martian surface and survive without the mandatory pressurized helmet to keep you from breathing in poisonous fumes. Everything would sound somewhat muffled to Earthling ears because of the quality of the atmosphere and an atmospheric chemistry that slightly lowers the speed of sound and in turn the sound pitch. Because sound is a pressure wave, made up of molecules that accumulate and disperse in wave patterns, it just wouldn’t be heard as loudly in such a thin atmosphere. This is what Bill Nye would sound like on Mars.
Now factor in Curiosity. The car-sized robotic rover’s 20-by-16-inch wheels, each driven by an electric motor that doesn’t make much sound at all (and still probably more sound than that rock), have holes designed to show backtracking scientists how far it has traveled, and creeps over the surface at a very non-rush hour .09 miles per hour to avoid being damaged by the Red Planet’s rocky terrain. It was the camera that monitors Curiosity’s health that spied the two-inch rock, which ended up trapped in there sliding up and down because it was too bulky to slip through the holes in the wheels.
Chemistry and density determine the speed of sound. In the thin, dry atmosphere of Mars, which is mostly carbon dioxide, that rock wouldn’t even make a minor scraping noise at the volume it would on our own planet. So what would it sound like?
While Curiosity couldn’t record the sound, it was probably a low-pitched scraping that wouldn’t exactly be the greatest science fiction sound effect. The Mars 2020 rover will go beyond that with its own built-in microphone to explore the alien sounds on Mars (think dust storms and lightning), which, if theorizing over this one tells us anything, are probably not that out of this world. But who knows—the future mission might pick up something never heard to human ears.